22 BACTERIOLOGY. 



bacteria, but upon the fact that the conditions of 

 life suffer no alteration. If the conditions fluc- 

 tuate, the bacteria will also vary in form and in 

 physiological activity. Individual bacteria as 

 well as their zooglceae or colonies always adapt 

 themselves to the " milieu" The constancy 

 which Koch's method revealed was not one of 

 true permanence of species, but rather one of 

 permanence of varieties due to station. As 

 one emigrant in his new home clings strenu- 

 ously to the manners and customs of his 

 fatherland while another quickly forsakes 

 them, so some species of bacteria transplanted 

 into changed conditions of life preserve their 

 original characteristics, while others part with 

 them. It is possible by means of pure cul- 

 ture to obtain proof of the validity of the prin- 

 ciple formulated by L. v. Buch and Moritz 

 Wagner, who maintained that by subjecting 

 individuals to different conditions of life, new 

 species might be produced. 



Bacteria can be separated readily into genera 

 and species, although earlier observers as- 

 sumed, that these organisms possessed an 

 almost limitless variability of form and of 

 physiological activity. There are certainly 

 some species which pass through compara- 

 tively few forms, although others are protean. 

 Of a kindred order of facts is the observation 



